Plasminogen mediates the atherogenic effects of macrophage-expressed urokinase and accelerates atherosclerosis in apoE-knockout mice

Abstract

Urokinase-type plasminogen activator (uPA) is expressed at elevated levels in atherosclerotic human arteries, primarily in macrophages. Plasminogen (Plg), the primary physiologic substrate of uPA, is present at significant levels in blood and interstitial fluid. Both uPA and Plg have activities that could affect atherosclerosis progression. Moreover, correlations between increased Plg activation and accelerated atherosclerosis are reported in several human studies. However, a coherent picture of the role of the uPA/Plg system in atherogenesis has not yet emerged, with at least one animal study suggesting that Plg is atheroprotective. We used a transgenic mouse model of macrophage-targeted uPA overexpression in apolipoprotein E-deficient mice to investigate the roles of uPA and Plg in atherosclerosis. We found that macrophageexpressed uPA accelerated atherosclerotic plaque growth and promoted aortic root dilation through Plg-dependent pathways. These pathways appeared to affect lesion progression rather than initiation and to include actions that disproportionately increase lipid accumulation in the artery wall. In addition, loss of Plg was protective against atherosclerosis both in the presence and absence of uPA overexpression. Transgenic mice with macrophagetargeted uPA overexpression reveal atherogenic roles for both uPA and Plg and are a useful experimental setting for investigating the molecular mechanisms that underlie clinically established relationships between uPA expression, Plg activation, and atherosclerosis progression.proteolysis ͉ aorta ͉ aneurysm

Mechanisms of Urokinase Plasminogen Activator (uPA)-mediated Atherosclerosis

“…We also showed using Plg Ϫ/Ϫ mice that accelerated atherosclerosis and aortic dilation in SR-uPA mice were mediated by uPA activation of Plg (15). However, our experiments also raise several issues.…”

“…Moreover, patients with evidence of increased Plg activation have an elevated risk for accelerated atherosclerosis and major cardiovascular events (8 -10), and uPA expression is elevated in aneurysmal human aortae (11,12). Important roles for uPA in atherosclerosis and aneurysm formation are supported by recent studies in our laboratory showing that 15-week-old Apoe Ϫ/Ϫ mice with macrophage-targeted uPA overexpression (SR-uPA ϩ/0 mice, with scavenger receptor promoter-driven expression of a uPA transgene) have significantly accelerated plaque growth and aneurysm forma-tion (13)(14)(15), older SR-uPA ϩ/0 Apoe Ϫ/Ϫ mice have increased atherosclerotic plaque rupture (16), and recipients of bone marrow transplants from uPA null mice have less atherosclerosis than recipients of bone marrow from uPA-expressing mice (14).…”

“…Western analysis of uPA in these same extracts was reported earlier (15). S100A9 was detected by Western analysis of extracts of peritoneal macrophages of 10-week-old SR-uPA ϩ/0 and nontransgenic mice (both Apoe Ϫ/Ϫ ).…”

“…Macrophage and Aortic Plasminogen Activator ActivityBone marrow-derived macrophages were obtained as described (15). On day 10 after plating, serum-free M199 medium was added and collected 20 h later.…”

“…These macrophages were obtained exactly as described above for the microarray study. Either 30 g (for the apoA-I blots) or 15 g (for the S100A9 blots) of protein were separated by SDS/PAGE and transferred to PVDF membranes (15). ApoA-I was detected with a rabbit antibody to mouse apoE that also reacts with apoA-I (1:1000; reference (35)), and bound antibody was detected with peroxidase-conjugated anti-rabbit IgG (1:10,000, Santa Cruz).…”